1. Field of the Invention
The present invention relates to a vascular-endothelial-cell-function evaluating apparatus that evaluates a function of vascular endothelial cells of a living subject.
2. Related Art Statement
Conventionally, the function of vascular endothelial cells of a living person is evaluated by imaging, using an ultrasound diagnostic device, a state in which blood vessels are dilated by administering a drug such as acetylcholine, or by pressing, using a cuff, a body portion of the person to stop a flow of blood in the body portion for several minutes and subsequently releasing the pressing of the cuff.
However, it is not recommended to administer any drugs in a living person. In addition, an ultrasound diagnostic device is expensive, and is not easy to use. Thus, the evaluation of vascular-endothelial-cell function is not practiced so widely.
It is therefore an object of the present invention to provide a vascular-endothelial-cell-function evaluating apparatus that can easily evaluate the function of vascular endothelial cells of a living subject.
The Inventors have carried out extensive studies and found that if a body portion of a living subject is pressed using a cuff, the diameter of blood vessels is changed by the pressing of the cuff, and that as the diameter of blood vessels is changed, a reflected-wave component of a pulse wave obtained from the cuff or a distal body portion of the subject located on a distal side of the cuff, is also changed. The Inventors have additionally found that the degree of change of the reflected-wave component of pulse wave that is caused by the change of diameter of blood vessels, depends on the condition of vascular endothelial cells of the subject. Here, the reflected-wave component of pulse wave mainly influences a waveform of a second half of a heartbeat-synchronous pulse of pulse wave, the second half being subsequent to a peak point of the pulse. Thus, the Inventors have finally found that the degree of change of pulse-wave-second-half information representing a characteristic of the second half of pulse wave, caused by the change of diameter of blood vessels, depends on the condition of vascular endothelial cells of the subject. The present invention has been developed based on these findings.
The above object has been achieved by the present invention. According to the present invention, there is provided a vascular-endothelial-cell-function evaluating apparatus comprising a pressing device including a cuff that is adapted to be worn on a first portion of a living subject, and a cuff-pressure changing device that changes a pressure in the cuff so as to press the first portion of the subject in a pressing period; a pulse-wave detecting device that detects a pulse wave including a plurality of heartbeat-synchronous pulses, from the first portion of the subject, or a second portion of the subject located on a distal side of the first portion; and a pulse-wave-second-half-information obtaining device that obtains a plurality of sets of pulse-wave-second-half information that represent respective characteristics of respective second-half portions of respective heartbeat-synchronous pulses of the pulse wave that are detected by the pulse-wave detecting device at respective different times, the respective second-half portions of the respective heartbeat-synchronous pulses being respective portions of the respective pulses that are subsequent to respective peak points of the respective pulses, the pulse-wave-second-half-information obtaining device providing a time-wise change of the sets of pulse-wave-second-half information that is caused by the pressing of the pressing device.
Here, the pressing period in which the cuff-pressure changing device changes the pressure in the cuff to press the first portion of the subject may be a prescribed time duration or a time duration defined by a prescribed operation such as a blood-pressure-measurement-related pressure changing operation, described later.
According to the present invention, the pulse-wave-second-half-information obtaining device obtains the plurality of sets of pulse-wave-second-half information, and provides the time-wise change of the sets of pulse-wave-second-half information that is caused by the pressing of the pressing device. It is possible to evaluate, based on the time-wise change of the sets of pulse-wave-second-half information, the function of vascular endothelial cells of the subject. Therefore, it is not needed to use an ultrasound diagnostic device and accordingly it is easy to evaluate the function of vascular endothelial cells.
According to a preferred feature of the present invention, the pressing device presses, with the cuff, the first portion of the subject so as to stop a flow of blood in the first portion, and subsequently decreases the pressure of the cuff down to a pressure not higher than a mean blood pressure of the first portion, and the pulse-wave-second-half-information obtaining device obtains the sets of pulse-wave-second-half information in a waveform-deformation period in which the pressure of the cuff has already been decreased to the pressure not higher than the mean blood pressure of the first portion and respective waveforms of the respective heartbeat-synchronous pulses of the pulse wave are deformed yet as a result of the pressing of the pressing device. According to this feature, in the waveform-deformation period in which the pressure of the cuff has already been decreased to the pressure not higher than the mean blood pressure of the first portion, after the cuff stops the flow of blood in the first portion of the subject, and the respective waveforms of the respective heartbeat-synchronous pulses of the pulse wave are deformed yet by the pressing of the pressing device, the pulse-wave-second-half-information obtaining device time-wise obtains the sets of pulse-wave-second-half information based on the respective waveforms of the respective heartbeat-synchronous pulses of the pulse wave detected by the pulse-wave detecting device. If the cuff stops the flow of blood in the first portion, the diameter of blood vessels decreases because no blood flows in the second portion located on the distal side of the cuff. However, thereafter, when the pressure of the cuff is decreased down to the pressure not higher than the mean blood pressure of the first portion, the diameter of blood vessels increases and temporarily exceeds an initial diameter in order to quickly supply blood to the second portion. Since the pulse-wave-second-half-information obtaining device time-wise obtains the sets of pulse-wave-second-half information after the pressure of the cuff has been decreased down to the pressure not higher than the mean blood pressure of the first portion, it can provide a great time-wise change of the sets of pulse-wave-second-half information. Thus, it is particularly easy to evaluate the function of vascular endothelial cells of the subject.
According to another feature of the present invention, the cuff-pressure changing device of the pressing device includes a blood-flow stopping device for increasing the pressure of the cuff up to a pressure higher than a systolic blood pressure of the first portion of the subject, so as to stop a flow of blood in the first portion; a first pulse-wave-detection-pressure keeping device for keeping, before the blood-flow stopping device increases the pressure of the cuff, the pressure of the cuff at a pulse-wave detection pressure not higher than a mean blood pressure of the first portion, for a time duration corresponding to at least one heartbeat of the subject; and a second pulse-wave-detection-pressure keeping device for keeping, after the blood-flow stopping device increases the pressure of the cuff, the pressure of the cuff at a pulse-wave detection pressure not higher than a mean blood pressure of the first portion, for a time duration corresponding to at least one heartbeat of the subject, the pulse-wave detecting device detects a cuff pulse wave that is transmitted from the first portion of the subject to the cuff, and the pulse-wave-second-half-information obtaining device obtains one of the sets of pulse-wave-second-half information from a cuff pulse wave detected by the pulse-wave detecting device in a state in which the pressure of the cuff is kept at the pulse-wave detection pressure by the first pulse-wave-detection-pressure keeping device, and obtains the other set of pulse-wave-second-half information from a cuff pulse wave detected by the pulse-wave detecting device in a state in which the pressure of the cuff is kept at the pulse-wave detection pressure by the second pulse-wave-detection-pressure keeping device. According to this feature, the pulse-wave-second-half-information obtaining device obtains the sets of pulse-wave-second-half information based on the respective pulse waves detected before the blood-flow stopping device stops the flow of blood in the first portion, and after the blood-flow stopping device completely stops the flow of blood in the first portion and subsequently sufficiently decreases the cuff pressure. Since the flow of blood in the first portion on which the cuff is worn is completely stopped once and subsequently the pressure of the cuff is sufficiently decreased, an amount of blood that flows in the second portion located on the distal side of the cuff temporarily exceeds an initial amount before the stopping. Therefore, it is possible to evaluate the function of vascular endothelial cells of the subject, based on a degree of change of the set of pulse-wave-second-half information obtained after the stopping, from the set of pulse-wave-second-half information obtained before the stopping.
According to another feature of the present invention, the cuff-pressure changing device of the pressing device further includes a pressure increasing device for increasing, before the first pulse-wave-detection-pressure keeping device keeps the pressure of the cuff at the pulse-wave detection pressure, the pressure of the cuff from a pressure lower than a diastolic blood pressure of the first portion of the subject, and the apparatus further comprises a pulse-wave-detection-pressure determining device for determining the pulse-wave detection pressure based on a fact that a deformation occurs to a waveform of a heartbeat-synchronous pulse of the cuff pulse wave continuously detected by the pulse-wave detecting device while the pressure of the cuff is increased by the pressure increasing device. According to this feature, the pulse-wave-detection-pressure determining device determines the pulse-wave detection pressure based on the pulse wave actually detected during the slow increasing of the cuff pressure. Thus, in each measuring operation, the most appropriate pulse-wave detection pressure is determined. Therefore, the respective pulse waves detected in the state in which the cuff pressure is kept at the pulse-wave detection pressure by the first pulse-wave-detection-pressure keeping device and in the state in which the cuff pressure is kept at the detection pressure by the second keeping device, have an accurate waveform, and accordingly the pulse-wave-second-half-information obtaining device obtains accurate sets of pulse-wave-second-half information based on the accurate pulse waves. Thus, it is possible to more accurately evaluate the function of vascular endothelial cells of the subject based on the accurate sets of pulse-wave-second-half information.
According to another feature of the present invention, the cuff-pressure changing device of the pressing device further includes a preliminary pressing device for increasing, before the first pulse-wave-detection-pressure keeping device keeps the pressure of the cuff at the pulse-wave detection pressure, the pressure of the cuff up to the pulse-wave detection pressure, by a predetermined number of times, so as to preliminarily press the first portion of the subject. According to this feature, the preliminary pressing device carries out the preliminary pressing of the first portion, and accordingly the cuff and the subcutaneous tissue of the first portion on which the cuff is worn are brought into close contact with each other. Therefore, a more accurate pulse wave can be detected and accordingly a more accurate set of pulse-wave-second-half information can be obtained based on the accurate pulse wave. Thus, it is possible to more accurately evaluate the function of vascular endothelial cells of the subject.
According to another feature of the present invention, the cuff-pressure changing device of the pressing device further includes a pressure increasing device for increasing, before the preliminary pressing device increases the pressure of the cuff, the pressure of the cuff from a pressure lower than a diastolic blood pressure of the first portion of the subject, and the apparatus further comprises a pulse-wave-detection-pressure determining device for determining the pulse-wave detection pressure based on a fact that a deformation occurs to a waveform of a heartbeat-synchronous pulse of the cuff pulse wave continuously detected by the pulse-wave detecting device while the pressure of the cuff is increased by the pressure increasing device.
According to another feature of the present invention, the blood-flow stopping device comprises a blood-pressure-measurement-related pressure changing device for increasing the pressure of the cuff up to the pressure higher than the systolic blood pressure of the first portion of the subject, and subsequently decreasing the pressure of the cuff, and the apparatus further comprises a blood-pressure determining device for determining a blood pressure of the subject based on a cuff pulse wave detected by the pulse-wave detecting device while the pressure of the cuff is decreased by the blood-pressure-measurement-related pressure changing device. According to this feature, the pulse-wave-second-half-information obtaining device time-wise obtains the sets of pulse-wave-second-half information of the subject, and additionally the blood-pressure determining device determines the blood pressure of the subject. Thus, it is possible to simultaneously evaluate the function of vascular endothelial cells, and obtain the blood pressure, of the subject.
According to another feature of the present invention, each of the sets of pulse-wave-second-half information comprises an augmentation index indicating a proportion of a reflected-wave component of the pulse wave to an incident-wave component thereof
According to another feature of the present invention, each of the sets of pulse-wave-second-half information comprises a degree of sharpness of the pulse wave.
According to another feature of the present invention, each of the sets of pulse-wave-second-half information comprises a diastolic area of the pulse wave.
According to another feature of the present invention, the vascular-endothelial-cell-function evaluating apparatus further comprises a heart-rate-related-information obtaining device that obtains a plurality of sets of heart-rate-related information each of which is related to a heart rate of the subject, based on respective heartbeat-synchronous pulses of the pulse wave that are detected by the pulse-wave detecting device at respective different times, the heart-rate-related-information obtaining device providing a time-wise change of the sets of heart-rate-related information that is caused by the pressing of the pressing device. According to this feature, it is possible to judge, based on a change of the sets of heart-rate-related information that is caused by the pressing of the pressing device, whether the activity of the autonomic nerve of the subject is normal. Thus, it is possible to simultaneously evaluate the function of the vascular endothelial cells, and the activity of the autonomic nerve, of the subject.